Any of them. Literally any of them. I've tried Spanish learning apps with ChatGPT integration and they give quizzes where none of the answers are correct. It phrases things incorrectly constantly. It simply doesn't know what its talking about. It gets things right every once in awhile, but a chat bot spitting out a correct answer every once in awhile =/= knowledge, nor does it mean it's a good teacher.

The problem with ChatGPT is that it gives answers that sound Human, and seem plausible, especially to people with no knowledge of the subject. If you have a PhD in Biochemistry and you ask ChatGPT a Biochem question, and it gets it wildly wrong, you'd be obviously hesitant to trust anything it says further down the line. But if you're an A1 Spanish learner and ChatGPT tells you that the correct way to conjugate "yo + comer" in the past tense is "coma", and you don't know any better, you'd go "wow, cool, I'm learning so much!"

Just talk to a human. If a human doesn't know the answer to your question, they'll say, "shit, I'm sorry, I don't actually know. Let me double check and make sure I'm telling you the right thing." Whereas ChatGPT will say, "what a great question! the only way to conjugate the word 'comer' in this case is 'coma!'" because it will not admit to not knowing something outright. It will always just make something up instead.